Complex, highly-integrated systems have become commonplace in many areas of technology. Examples of highly-integrated systems include mobile vehicles such as modern fast jet fighters and civilian airliners, unmanned aerial vehicles, industrial structures such as power plants, chemical plants and off-shore oil and gas platforms, and large-scale experimental apparatus such as particle accelerators and fusion reactors. Each of these systems can be considered as a platform that hosts a large number of sub-systems, each sub-system being arranged to perform a specific function of the overall system and to communicate with other sub-systems as necessary. The sub-systems may share common resources of the platform, such as in a so-called ‘tightly coupled’ system, or sub-systems may be essentially independent of one another.
By way of example, FIG. 1 shows, schematically, the major systems and sub-systems in a generic military aircraft (adapted from Moir and Seabridge, “Design and Development of Aircraft Systems”, Professional Engineering Publishing, ISBN 978-1-86058-437-4). The aircraft platform 100 hosts a plurality of sub-systems 102. The sub-systems 102 are grouped into four system categories 104, according to the general function to which the sub-systems contribute. For example, the vehicle systems category includes the sub-systems responsible for propulsion, fuel storage and supply, flight control, landing gear and so on.
Many of the sub-systems 102 depend on other sub-systems 102 for their operation. For instance, the propulsion sub-system depends upon the fuel sub-system to supply fuel to the propulsion device. The fuel sub-system is, in turn, linked to a fire protection sub-system, which can selectively shut off the fuel supply in the event of a fire.
It will be appreciated from FIG. 1 that the aircraft platform 100 includes a large number of such inter-connected and inter-dependent sub-systems 102, many of which are critical to the ability of the aircraft to complete an assigned task safely and effectively. It is therefore desirable to monitor the condition of each sub-system 102 of the platform 100, so that the ability of the platform 100 to perform as required can be assessed.
In one context, monitoring the condition of the sub-systems of a platform is important in providing real-time diagnostic information to the operator of the platform, and to other sub-systems of the platform, about faults that have appeared in a sub-system. In this way, when a fault in a sub-system is detected, appropriate action can be taken to minimise the impact of the fault on the safety and operation of the platform and the success of the task it is performing. The diagnostic information can also be used to schedule maintenance of the platform, and to facilitate efficient repair of the platform through service and maintenance operations.
In another context, information about the condition of the sub-systems of a platform can be used in a prognostic manner. By analysing information about the condition of sub-systems of a platform during use, such as by collating historical information and developing models of behaviour, it is possible to predict more accurately the need for preventative maintenance, replacement of parts and so on, and to design more effectively the logistics supply chain required for supporting the platform. As a result, the costs of supporting the platform can be reduced by avoiding unnecessary maintenance, and the availability and reliability of the platform can be increased by minimising in-service failures and unscheduled maintenance.
Platform condition monitoring in the prognostic context is becoming increasingly valuable. The cost of keeping a complex platform available for use and mission-capable throughout its service life can be substantial and, as the complexity of platforms increases, there is an increasing desire to reduce or limit these through-life asset costs by providing an effective and efficient support and maintenance regime. Furthermore, it is becoming increasingly common for customers to lease platforms from manufacturers, rather than purchasing the platform and a support agreement. This arrangement, sometimes known as availability contracting, shifts the burden of through-life asset costs from the customer to the manufacturer, making it commercially important to consider integrating a means for monitoring the condition of sub-systems into the design of new platforms. Equally, it is important to consider adding such means to existing ‘legacy’ platforms.
It is known in the art to provide platforms with a sub-system that is capable of monitoring the condition, or ‘health’, of the sub-systems of a platform, and delivering the health information to operators, service personnel and other interested parties. Such systems are variously known in the art as integrated vehicle health management systems, health utilisation/usage monitoring/management systems, abnormal event detectors and diagnostic and prognostic systems. Systems of this type will be referred to hereafter as health management systems.
Design and development of a health management system for a new platform can be undertaken independently from the design of the platform itself. The result can be an inadequately integrated support capability. In the case of legacy platforms, a health management system can be designed on an ad-hoc basis and added to a legacy platform as required. However, designing a health management system for a legacy platform, or for a particularly complex new platform, can be problematic. For example, it can be difficult to elucidate the specifications (e.g. informational requirements) for a health management system, in terms of information that should or must be obtained, processed and output by the health management system so as to fulfil the needs of operators, service personnel and other users of the system.
Furthermore, without a clear understanding of these information specifications, it becomes difficult to produce a design for a health management system, in terms of the sub-systems that must or should be monitored, the sensors to be used for such monitoring, and the data processing to convert the output of such sensors into the desired information.
Against this background, it would be desirable to provide a method for designing a health management system that can address (e.g. overcome or mitigate) the above-mentioned issues and, correspondingly, a health management system having a structure that facilitates its design in such a way as to address these issues.